shock and awe

i think i mentioned to you that i recently bought a bike. i thought when i got it the rear suspension was spongier than i wanted it, but i figured to adjust it. no biggie, right? so then after the crash i pumped up the shock, because it was spongy. and it was nice and snappy until i rode it. and then it wasn't snappy. it was saggy and the shock was only holding 150 psi. i weigh 200 pounds, so i ought to be riding that shock at about 180, give or take a little. but i don;t know a lot about shocks, so i tested and repumped and had someone else test and check it but it holds 150 psi and that's it. into the shop. out of the shop. the took the shock apart and found nothing but dry seals, lubed the seals and sent me home with it. then more leaking to 150 psi. back to the shop. they replaced the shock. two days riding, and it's spongy! another shock dropping to 150 psi. i am getting frustrated. if a shock doesn't hold air, it should not hold air, not just not hold any air over 150 psi. if one shock does that, it's a freak thing. if two shocks do that, it's a challenge to my concept of reality. what is going on????